Polychlorinated biphenyls (PCBs) and the DDT/DDE (DDE is the stored metabolite of DDT) family are toxic, widespread pollutants. Both pass from mother to child through the placenta and by contaminating breast milk. This project includes a study of subjects exposed to low levels of both compounds in North Carolina, a study in Mexico where levels of DDE are two to five times higher, and a study of persons poisoned by PCBs in Taiwan. PCBs and DDE can cause long term induction of steroid metabolizing enzymes. In North Carolina, we have collected data on onset of puberty in a cohort of children we have followed since 1978. In Mexico, in a preliminary analysis, we found that women who have higher levels of DDE in breast milk have shorter lactations, and we are finishing detailed analyses of those data. This is similar to what we found previously in North Carolina, and may be a result of the estrogenicity of o,p-DDE, since estrogens decrease milk volume. In Taiwan, an epidemic of 2000 cases of PCB poisoning occurred in 1979. We have completed follow-up of about 90% of the cohort, and have begun mortality analyses.